Step 1: Understanding the Question:
We need the main reason behind the huge win of the Congress in the 1951-52 general election.
Step 2: Key Fact or Approach:
The Congress had led the freedom struggle and was a broad party. It was a rainbow-like coalition that took in all classes, castes, religions and regions, and that all-inclusive nature gave it its large base.
Step 3: Check option 1.
The election was a multi-party contest, but that does not explain the Congress victory. Communal riots at the time of Partition did not help it win in this way. So this is not the reason. So option 1 is WRONG.
Step 4: Check option 2.
Congress support came from all over the country, in rural and urban areas, and from all regions. It was not limited to urban areas in Hindi speaking states. So option 2 is WRONG.
Step 5: Check option 3.
The Congress brought together farmers, workers, industrialists, many castes and religions and several ideologies. This inclusive nature was the main reason for its success. So option 3 is CORRECT.
Step 6: Check option 4.
The Congress did not lead any agitation to replace English with Hindi. This is not a reason for its win in 1952. So option 4 is WRONG.
Final Answer:
The all-inclusive nature of the Congress explains its success, which is option 3.
\[ \boxed{\text{Option 3}} \]